People are generally aware of the most common causes of hallucinations, like schizophrenia and a really high fever. But lesser known are the more rare causes; here are six you probably haven't heard about.

Woman Suffered 'Heart Attack' for 14 Years

At 42 years old, Dorothy Asquith suddenly began having crushing chest pains. Suspecting a heart attack, Asquith was rushed to the hospital, but tests showed that her arteries were perfectly normal and clear of blockages. Indeed, Asquith had always been perfectly healthy before her sudden chest pain.

But the pain remained for 14 years, and her trips from doctor to doctor failed to reveal what was wrong. The pain would persist for two to three weeks at a time, then disappear as suddenly as it had appeared.

The pain medication did not work, and her quality of life evaporated. The mysterious condition took a severe toll on her personal life; she and her husband briefly separated.

Finally, doctors determined the cause: cardiac syndrome X. The rare and little-understood condition causes intense pain like that experienced during a heart attack or angina. It affects an estimated 12,000 people.

Those other cardiac conditions, though, are caused by blood blockages that block oxygen off from the heart. Cardiac syndrome X, on the other hand, does not have any apparent physical causes. Indeed, many sufferers of the condition are told that it is all in their head.

Researchers do believe that the condition is real, however, and are starting to identify the causes. A recent study with magnetic resonance imaging (MRI) machines found that, in about a third of patients with cardiac syndrome X, the tiny blood vessels did not open correctly, cutting off some blood supply. Researchers theorize that, because the flow of oxygen is cut off, it causes intense heart pain. Because the small vessels are only seen on MRI machines, they may not be spotted through conventional methods, like ultrasounds and angiograms.

The condition is not considered life-threatening and doesn't raise heart attack risk.

Another theory is that the condition is caused by the loss of estrogen. Ms. Asquith had a hysterectomy the year before her symptoms began, and many sufferers' symptoms appear during the onset of menopause. Indeed, the condition appears in nine times as many women as it does in men. The drop of estrogen may trigger symptoms in patients at risk, or the loss of estrogen may reduce the body's ability to block pain.

Patients are treated in various manners. Beta blockers and calcium channel blockers increase the flow of blood to the heart. Asthma and blood-pressure medication open up small blood vessels. Antidepressants can also be used to reduce pain.

A new option is hypnotherapy to help patients change the way that their body responds to pain. Asquith says that hypnotherapy has helped her a lot. Whenever she feels an episode coming on, she pictures the beach. She has not had any pain since her eight-week treatment.